We describe an integrated and compositional technique, together with its supporting toolset, for hardware/software co-design. The co-design process is soundly based upon formal techniques, but includes integrated support for simulation. A unique characteristic of our framework is that it can validate and analyse system's behaviours of interest compositionally and within a single logical formalism, namely Interval Temporal Logic (ITL) and its executable subset, (Ana)Tempura. The paper presents voice over IP as an application to our framework.